The present invention relates to novel organofunctional imidesilane coupling agents which exhibit exceptionally high thermal stability and outstanding coupling effectiveness in composites consisting of a polyimide resin matrix and a mineral oxide substrate. The invention also relates to the methods of synthesizing, isolating and employing the compounds in polyimide-mineral oxide composites.
In producing integrated circuits, use is made frequently of a silica substrate to which is adhered a patterned polyimide wash to provide dielectric isolation. Frequently, these circuits are formed at elevated temperatures of up to about 300.degree. C. or higher which requires that adhesion promoters utilized in the circuit formation provide strong bonding and are thermally stable. Extensive research has been carried out to develop silane coupling agents for high temperature resins. For example, numerous reactive organofunctional aromatic silanes have been evaluated [e.g., Pleuddemann, Proceedings, 22nd Annual Meeting of the Reinforced Plastics Division of the Society of the Plastics Industry, Sec. 9-A, p. 1 (1967)] and a ranking of thermal stability has been proposed. More recently, ethylene bridged aromatic silanes have been suggested as high temperature coupling agents [B. Arkles and W. Peterson, Proceedings, 35th Annual Technical Conference. Reinforced Plastics Composites Institute, SPI (1980)]. However, known compounds have not exhibited the balance of properties required in commercial applications of composites comprising polyimide resins and films and a mineral oxide substrate. These properties include solubility, reactivity, interpenetrating compatibility of the polymer formed at the interface with the polyimide and the high adhesive strength at the interface retained upon exposure of the composite to elevated temperature.
Attempts have been made to incorporate amino-functional silanes in polyimide resins in order to improve the adhesive strength of the modified polymers in composites without pretreatment of the substrate with adhesion promoters. Such "integral mix" coupling approaches, in which coupling agents were not isolated, characterized and separately applied, disclosed, for example, in German Offenlegungsschrift No. 2,838,874 and in U.S. Pat. No. 4,161,477, have many limitations and do not represent a solution to the problem of thermally stable coupling agents for polyimide composites.
It would be desirable to provide coupling agents for effecting adhesion between a polyimide and a mineral oxide substrate which effect a strong bond and which are thermally stable. Such coupling agents would facilitate the production of the composite products, particularly integrated circuits.